Method for preparing formic acid through three-chamber two-membrane electrolysis of CO2

Abstract

The invention belongs to the technical field of electrolytic synthesis, and particularly relates to a method for preparing formic acid through three-chamber two-membrane electrolysis of CO2. The method is based on a three-chamber two-membrane electrolysis device which is divided into an anode chamber, a middle chamber and a cathode chamber by a cationic membrane and a nanofiltration membrane, a concentrated KOH aqueous solution is added into the anode chamber, a dilute KOH solution is added into the middle chamber, and CO2 and water are introduced into the cathode chamber; and after a power supply is switched on for full reaction, dilute KOH solutions are obtained in the anode chamber and the intermediate chamber respectively, and a KCOOH product is obtained in the cathode chamber. According to the method, the utilization rate of CO2 is remarkably increased, the electrolysis power consumption is reduced, the problems of water logging and the like are avoided, and the operation life is greatly prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolytic synthesis, and particularly relates to a production method for preparing formic acid by electrolyzing CO2. BACKGROUND

[0002] Since the industrial revolution, the overuse of fossil fuels (coal, oil, natural gas, etc.) has caused the CO2 content in the atmosphere to rise year by year, which has seriously exceeded the limit of the carbon cycle in nature, causing a series of environmental problems such as rising temperature and climate change.

[0003] The CO2 conversion methods include chemical reforming method, photocatalytic method, biological method, and electrocatalytic reduction method. Among them, the electrochemical CO2 conversion can be carried out at room temperature and ambient pressure, and can obtain higher conversion efficiency. The products of electrochemical reduction of CO2 are numerous, and HCOOH and CO only need to transfer 2e-, which has low power consumption, and is the main research product. HCOOH is one of the commonly used chemical raw materials, and has wide industrial applications, such as plastics, pharmaceuticals, leather, etc.

[0004] In the electrolysis of carbon dioxide, a gas diffusion electrode is often used to promote the mass transfer rate of the reaction and thus accelerate the reaction rate. Compared with the traditional bulk electrode, the reaction rate of the gas diffusion electrode can be improved by more than two orders of magnitude. The existing gas diffusion electrode is mainly based on a carbon substrate (such as commercial carbon fiber paper, carbon cloth, etc.), and a small amount of catalyst is further loaded on the carbon substrate. However, the gas diffusion electrode based on carbon substrate has low strength and insufficient hydrophobic mass to meet the problem of maintaining hydrophobicity for a long time, resulting in low service life of the gas diffusion electrode. If it is popularized to industrial use, the cost of electrode material will be greatly increased.

[0005] At present, the method for electrochemically reducing CO2 to prepare formic acid is limited by the problems of low electrode service life or high power consumption, and the cost of electrochemical preparation of formic acid from CO2 is high, which is difficult to popularize to industrialization.

[0006] In addition, in the electrochemical reduction of CO2, the anode is mostly for oxygen evolution reaction, which produces oxygen without commercial value, and only the cathode reaction is used in the electrolysis process to produce valuable products. If the anode and cathode are combined for co-electrolysis, the anode produces products with added value, which will have high economic value and reduce the power consumption of CO2 electrolysis.

[0007] Therefore, in order to solve the problem of low electrolysis efficiency of electrochemical preparation of formic acid from CO2, and realize the effective utilization of the anode, a method that can meet the requirements of high efficiency, low cost and industrialization for electrochemical reduction of CO2 needs to be developed. SUMMARY

[0008] The technical problem solved by the present application is to overcome the defects of low utilization rate and high electrolysis power consumption in the prior art of preparing formic acid by electrolysis of CO2, thereby providing a method for preparing formic acid by electrolysis of CO2 in three chambers and two membranes.

[0009] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0010] A method for preparing formic acid by electrolysis of CO2 in three chambers and two membranes, comprising:

[0011] Based on an electrolysis device with a cation membrane and a nanofiltration membrane, the cation membrane and the nanofiltration membrane separate the electrolytic cell into an anode chamber, an intermediate chamber and a cathode chamber; an anode plate is arranged on the side of the anode chamber away from the cation membrane, and a cathode plate is arranged on the side of the cathode chamber away from the nanofiltration membrane; the anode plate and the cathode plate are connected with a power supply;

[0012] A first KOH aqueous solution is added to the anode chamber, a second KOH aqueous solution is added to the intermediate chamber, and CO2 and water are introduced into the cathode chamber; after the power supply is turned on and fully reacted, KOH solutions are obtained in the anode chamber and the intermediate chamber, and a KCOOH product is obtained in the cathode chamber.

[0013] In some specific embodiments, the cation membrane is one or more of a sulfonic acid type, a phosphoric acid type, a carboxylic acid type and a composite cation membrane.

[0014] In some specific embodiments, the mass concentration of the first KOH aqueous solution is higher than that of the second KOH aqueous solution, and preferably the absolute value of the concentration difference is not less than 2%;

[0015] Preferably, the mass concentration of the first KOH aqueous solution is 5-9%, and the mass concentration of the second KOH aqueous solution is 5-7%;

[0016] More preferably, the mass concentration of the KOH solution obtained in the anode chamber is lower than that of the first KOH aqueous solution, and the mass concentration of the KOH solution obtained in the intermediate chamber is higher than that of the second KOH aqueous solution.

[0017] Further preferably, the mass concentration of the KOH solution obtained in the anode chamber is 3-7%, and the mass concentration of the KOH solution obtained in the intermediate chamber is 7-9%.

[0018] In some specific embodiments, the nanofiltration membrane is a modified nanofiltration membrane, and the modification method is as follows:

[0019] S1, add a quaternary amine base, a complexing agent and a pH buffer to silicon carbide powder, obtain a stable dispersion by ultrasonic treatment, then heat and stir the solution to fully mix it, wash the obtained mixture with deionized water and alcohol until the solution is neutral, dry, crush and sieve 1000-2000 meshes to obtain a nano silicon carbide powder with a surface modified quaternary amine base;

[0020] S2, mixing the polyolefin ester monomer, the nano-silicon carbide powder of the surface modified quaternary ammonium base, and the polytetrafluoroethylene resin uniformly, and mixing uniformly by ultrasonic treatment to obtain the hydrophilic polytetrafluoroethylene resin;

[0021] S3, melt blending the hydrophilic polytetrafluoroethylene resin with a lubricant to obtain a modified polytetrafluoroethylene emulsion, and then extruding through an extruder, cooling and forming, extracting and removing solvent, high-temperature bidirectional stretching, and high-temperature sintering and curing to obtain a modified polytetrafluoroethylene base film;

[0022] S4, soaking the modified polytetrafluoroethylene base film in an aqueous solution of trimethyladamantyl ammonium hydroxide, then drying the modified polytetrafluoroethylene base film, laying it flat, uniformly coating the prepared homogeneous casting solution on the modified polytetrafluoroethylene base film, standing, drying and curing, and cleaning to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

[0023] In some specific embodiments, the quaternary ammonium base in step S1 is selected from at least one of benzyltrimethylammonium hydroxide, hexamethonium hydroxide, and trimethyladamantyl ammonium hydroxide, preferably benzyltrimethylammonium hydroxide; the complexing agent is selected from at least one of EDTA, iminodiacetic acid, and nitrilotriacetic acid (NTA), preferably EDTA; and the pH buffer is selected from at least one of Na2HPO4 and KH2PO4, preferably Na2HPO4;

[0024] Preferably, the concentration of the quaternary ammonium base is 2-5 mol / L, the concentration of the complexing agent is 10-100 mol / L, and the concentration of the pH buffer is 4-25 mol / L;

[0025] More preferably, the mass ratio of the quaternary ammonium base, the complexing agent, and the pH buffer is 1:5:2-1:20:5;

[0026] In step S1, the ultrasonic treatment time is 1-1.5 h, and then the solution is heated to 60-90°C and stirred for 2-4 h.

[0027] In some specific embodiments, the ultrasonic treatment temperature in step S2 is 60-130°C, and the treatment time is 20-60 min;

[0028] Preferably, the high-temperature sintering temperature in step S3 is 330-360°C, and the sintering time is 10-20 min;

[0029] Preferably, the soaking time in step S4 is 60-480 min, the standing time is at least 10 min, the drying and curing temperature is 50-80°C, and the drying time is 1-3 h.

[0030] In some specific embodiments, the anode chamber, the intermediate chamber and the cathode chamber are independent of each other, and the operating temperature is 40-50℃.

[0031] In some specific embodiments, the anode plate is one or more of a nickel plate, a DSA plate and a graphite material.

[0032] In some specific embodiments, the cathode plate is one or more of a nickel plate and a graphite material.

[0033] Preferably, the cathode plate is soaked in a tellurium salt, a copper salt or a molybdenum salt at high temperature for 1-3h before use.

[0034] More preferably, the tellurium salt, the copper salt or the molybdenum salt is a nitrate salt at a concentration of 0.2-2mol / L.

[0035] In some specific embodiments, the current density of the electrolysis device is 1500-2500A / mm 2 , and the residence time is 20-60min.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] 1) The present application is based on a three-chamber two-membrane electrolysis device with a cation membrane and a modified nanofiltration membrane, which is used to electrolytically reduce CO2 to prepare formic acid. The nanofiltration membrane is modified with a benzyl trimethyl quaternary amine base functional group, which increases the selectivity and conductivity of the electrolysis reaction. The nanofiltration membrane substrate and the coated homogeneous casting solution are combined using trimethyladamantyl ammonium hydroxide, which improves the composite property of the membrane and increases the reaction selectivity.

[0038] 2) The cathode electrode of the present application increases the ternary catalytic sites of tellurium, copper and molybdenum, which further improves the conductivity and reduces the electrolysis voltage. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 is a structural schematic diagram of the electrolysis device provided in the embodiments of the present application.

[0041] Among them, 1 is the anode chamber, 2 is the intermediate chamber, 3 is the cathode chamber, 4 is the cation membrane, 5 is the nanofiltration membrane, 6 is the anode plate, and 7 is the cathode plate. DETAILED DESCRIPTION

[0042] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0043] like Figure 1 As shown, based on an electrolysis device with a cation exchange membrane 4 and a nanofiltration membrane 5, the cation exchange membrane 4 and the nanofiltration membrane 5 divide the electrolysis cell into an anode chamber 1, an intermediate chamber 2, and a cathode chamber 3; an anode plate 6 is provided on the side of the anode chamber 1 away from the cation exchange membrane 4, and a cathode plate 7 is provided on the side of the cathode chamber 3 away from the nanofiltration membrane 5; the anode plate 6 and the cathode plate 7 are connected to a power source; a concentrated KOH aqueous solution is added to the anode chamber, a dilute KOH solution is added to the intermediate chamber, and CO2 and water are introduced into the cathode chamber; after the power source is turned on and the reaction is complete, a KOH solution that is more dilute than the feed is obtained in the anode chamber and a KOH solution that is more concentrated than the feed is obtained in the intermediate chamber, and KCOOH product is obtained in the cathode chamber.

[0044] In this invention, the cation exchange membrane is one or more of sulfonic acid type, phosphoric acid type, carboxylic acid type and composite type cation exchange membranes, all of which are commercially available products.

[0045] In this invention, the nanofiltration membrane is a modified nanofiltration membrane, and an exemplary modification method is as follows:

[0046] S1. Add 2-5 mol / L benzyltrimethylammonium hydroxide, 0.5-3 mol / L EDTA, and 1-6 mol / L Na2HPO4 to silicon carbide powder (>1000 mesh). Obtain a stable dispersion by ultrasonic treatment at room temperature for 1-1.5 h. Then heat the solution to 60-90℃ and stir for 2-4 h to mix it thoroughly. Wash the mixture 2-3 times with deionized water and ethanol until the solution is neutral. After drying, pulverizing, and sieving through a 1000-2000 mesh, obtain surface-modified benzyltrimethylammonium carbide nanoparticles.

[0047] S2. Prepare hydrophilic polytetrafluoroethylene resin by mixing polyvinyl acetate, surface-modified nano silicon carbide powder, and polytetrafluoroethylene (mass ratio of 1:1:1 to 1:4:6) evenly, and then ultrasonically treat the mixture at 60 to 130°C for 20 to 60 minutes to obtain the hydrophilic polytetrafluoroethylene resin.

[0048] S3. Hydrophilic polytetrafluoroethylene resin and lubricant are melt-blended to obtain modified polytetrafluoroethylene emulsion, which is then extruded, cooled and shaped, extracted, biaxially stretched at high temperature and sintered and cured at high temperature of 330-360℃ for 10-20 min to prepare modified polytetrafluoroethylene film.

[0049] S4, soaking the modified polytetrafluoroethylene base film (mass ratio of 1:60-1:100) with trimethyladamantane ammonium hydroxide solution for 60-480 min to improve the affinity of the base film and the emulsion, then drying the modified polytetrafluoroethylene base film and laying it flat, uniformly coating (10-100 μm thick) the prepared homogeneous casting solution on the modified polytetrafluoroethylene base film, standing and drying for 10 min, and then drying and curing in a vacuum drying oven at 50°C for 1-3 h, and then washing to obtain the modified polytetrafluoroethylene composite nanofiltration membrane.

[0050] Among them, the lubricant is a commonly used lubricant in the art, such as Henglo Letai 30138, 3M Dyneon TF9205, etc. The homogeneous casting solution is a commonly used homogeneous casting solution in the art, such as being configured according to the mass ratio of polysulfone:N,N-dimethylformamide:water = 1:20:1-1:50:2.

[0051] In the present application, the anode chamber, the intermediate chamber and the cathode chamber are independent of each other and only allow corresponding ions to pass through, and the operating temperature of the entire electrolytic cell is 40-50°C.

[0052] In the present application, the anode plate is a commonly used positive electrode material in the art, such as one or more of nickel plate, DSA plate and graphite material; the cathode plate is a commonly used cathode material, such as one or more of nickel plate and graphite material, and the cathode plate of the present application is soaked in tellurium, copper and molybdenum salt (0.2-2 mol / L nitrate) at high temperature for 1-3 h before use to increase the electrical conductivity and reduce the operating voltage.

[0053] In the examples, if the specific experimental steps or conditions are not specified, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagents or instruments used are not specified by the manufacturer, they are all conventional reagent products that can be obtained by purchase.

[0054] The main raw materials involved in the following examples are as follows:

[0055] Raw materials Company Specification Silicon carbide powder Jinmeng New Material 0.5 μm specification Benzyltrimethylammonium hydroxide Kent Catalytic Materials 25% specification Hexamethonium hydroxide Kent Catalytic Materials 25% specification Trimethyladamantylammonium hydroxide Kent Catalytic Materials 25% specification Polytetrafluoroethylene resin Solvay 6-10 microns

[0056] Other conventional chemical reagents were purchased from Inokai.

[0057] The main test methods involved in the following examples are as follows:

[0058] CO2 conversion rate = m 甲酸钾 / M 甲酸钾 / m CO2进气量 *Mco2

[0059] The CO2 inlet and outlet quantities are measured by mass flow meters.

[0060] The content of potassium carbonate and potassium formate is determined by acid-base titration method, and the specific method refers to GB / T 1587-2016.

[0061] The electrolysis operating current is a parameter of active control, and the voltage is the real-time display number of the electrolytic cell.

[0062] The operating life is the total operating time from the start of electrolysis to the 30% increase in electrolysis voltage.

[0063] Example 1

[0064] The electrolytic device as shown in Figure 1 is used to prepare formic acid from CO2, wherein;

[0065] The modification method of the nanofiltration membrane is as follows:

[0066] S1, add 1L of a solution containing 2mol / L of benzyltrimethylammonium hydroxide, 10mol / L of EDTA, and 4mol / L of Na2HPO4(mass ratio of 1:3.3:29.2:5.7) to the silicon carbide powder (>1000 mesh, 100g), and treat by ultrasonic (60W) at room temperature for 1h to obtain a stable dispersion. Then heat the solution to 60℃ and stir for 2h to fully mix. Wash the obtained mixture with deionized water and ethanol for 2 times until the solution is neutral. Dry, crush, and sieve to 1000 mesh to obtain the surface-modified nanometer boron nitride powder;

[0067] S2, uniformly mix polyvinyl acetate, surface-modified nanometer silicon carbide powder, and polytetrafluoroethylene (mass ratio of 1:1:1) to prepare a hydrophilic polytetrafluoroethylene resin. Ultrasonic treat at 60℃ for 20min to mix uniformly, and obtain the hydrophilic polytetrafluoroethylene resin;

[0068] S3, melt blend the hydrophilic polytetrafluoroethylene resin with 5wt% of lubricant (Henggao Loctite 30138) based on the mass of the polytetrafluoroethylene resin to obtain a modified polytetrafluoroethylene emulsion. Then extrude through an extruder, cool and shape, extract, high-temperature bidirectional stretch, and high-temperature sintering and curing at 330℃ for 10min to prepare a modified polytetrafluoroethylene base film.

[0069] S4, soak the modified polytetrafluoroethylene base film in an aqueous solution of trimethyladamantane ammonium hydroxide (mass ratio of 1:60) for 60min to improve the affinity of the base film and the emulsion. Dry the modified polytetrafluoroethylene base film, lay it flat, and uniformly coat (10μm thick) a prepared homogeneous casting solution (mass ratio, polysulfone:N,N-dimethylformamide:water=1:30:1.8) on the modified polytetrafluoroethylene base film. After standing and drying for 10min, dry and cure in a vacuum drying oven at 50℃ for 1h. After the heat treatment is completed, wash to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

[0070] All material chambers, anode chamber, cathode chamber are independent of each other, and the operating temperature is 40℃.

[0071] The positive plate of the electrolytic cell is a nickel plate, the cation membrane material is a sulfonic acid type Nafion membrane (Nafion N115, Shanghai Hesen Electrical Co., Ltd.), the cathode plate is a nickel plate, and the cathode plate is treated with tellurium, copper and molybdenum salts (all 0.2 mol / L nitrate) at high temperature for 1 h before use to increase the conductivity and reduce the operating voltage. The current density is 1500 A / m 2 , and the residence time of the electrolytic cell is 20 min.

[0072] The cathode chamber of the electrolytic cell is supplied with 100 mL / min CO2 gas, and the pressure is 0.6 MPa. The KOH concentration of the anode chamber feed is 9 wt%, and the concentration of the discharge is 5 wt%. The KOH concentration of the intermediate chamber feed is 5 wt%, and the concentration of the discharge is 7 wt%. The pressure is 0.25 MPaG.

[0073] Example 2

[0074] The electrolytic device as shown in Figure 1 is used to prepare formic acid from CO2, wherein the modification method of the nanofiltration membrane is as follows:

[0075] S1, add 1L of a solution containing 5mol / L of benzyltrimethylammonium hydroxide, 100mol / L of EDTA, and 25mol / L of Na2HPO4 (i.e. mass ratio of 1:8.4:292.2:39.5) to the silicon carbide powder (>1000 mesh, 100g), and treat by ultrasonic (100W) at room temperature for 1.5h to obtain a stable dispersion. Then heat the solution to 90℃ and stir for 4h to fully mix. Wash the obtained mixture with deionized water and ethanol for 3 times until the solution is neutral. Dry, crush, and sieve to 2000 mesh to obtain the surface-modified nanometer boron nitride powder;

[0076] S2, uniformly mix polyvinyl acetate, surface-modified nanometer silicon carbide powder, and polytetrafluoroethylene (mass ratio of 1:2:2) to prepare a hydrophilic polytetrafluoroethylene resin, and uniformly mix by ultrasonic treatment at 130℃ for 60min to obtain the hydrophilic polytetrafluoroethylene resin;

[0077] S3, melt blend the hydrophilic polytetrafluoroethylene resin with 5wt% of lubricant (3M Dyneon TF 9205) based on the mass of the polytetrafluoroethylene resin to obtain a modified polytetrafluoroethylene emulsion, and then extrude through an extruder, cool and shape, extract, high-temperature bidirectional stretch, and high-temperature sintering and curing at 360℃ for 20min to prepare a modified polytetrafluoroethylene-based membrane;

[0078] S4, soak the modified polytetrafluoroethylene base film (mass ratio 1:80) in an aqueous solution of hexamethonium hydroxide for 480 min to improve the affinity of the base film and the emulsion, then dry the modified polytetrafluoroethylene base film and lay it flat, uniformly coat (1000 μm thick) the prepared homogeneous casting solution (mass ratio, polysulfone: N, N-dimethylformamide: water = 1:40:1.2) on the modified polytetrafluoroethylene base film, let it stand and dry for 10 min, then dry and cure it in a vacuum drying oven at 80°C for 3 h, and then wash it to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

[0079] All material chambers, anode chambers, and cathode chambers are independent of each other, and the operating temperature is 50°C.

[0080] The positive plate of the electrolytic cell is a graphite material, the cation membrane material is carboxylic acid type F-893 (Asahi), the negative plate is a graphite material, and before use, the negative plate is treated with tellurium, copper, and molybdenum salts (2 mol / L nitrate) at high temperature for 3 h to increase the electrical conductivity and reduce the operating voltage. The current density is 2500 A / m 2 , and the residence time of the electrolytic cell is 60 min.

[0081] The cathode chamber of the electrolytic cell is supplied with 100 mL / min CO2 gas at a pressure of 0.6 MPa, the anode chamber is fed with KOH at a concentration of 9 wt%, and the discharge concentration is 7 wt%, the intermediate chamber is fed with KOH at a concentration of 5 wt%, and the discharge concentration is 9 wt%, and the pressure is 0.25 MPaG.

[0082] Example 3

[0083] An electrolytic device as shown in Figure 1 is used to prepare formic acid from CO2, wherein;

[0084] The modification method of the nanofiltration membrane is as follows:

[0085] S1, add 1 L of a solution containing 3 mol / L of benzyltrimethylammonium hydroxide, 30 mol / L of iminodiacetic acid, and 9 mol / L of KH2PO4 (i.e., mass ratio 1:5.0:39.9:12.2) to silicon carbide powder (>1000 mesh, 100 g), and obtain a stable dispersion by ultrasonic treatment (60 W) at room temperature for 1.2 h, then heat the solution to 80°C and stir for 3 h to fully mix, wash the obtained mixture with deionized water and ethanol twice until the solution is neutral, dry, crush, and sieve >1000 mesh to obtain surface-modified nanometer boron nitride powder;

[0086] S2, hydrophilic polytetrafluoroethylene resin is prepared by mixing polyvinyl acetate, surface-modified nanometer silicon carbide powder and polytetrafluoroethylene (mass ratio 1:3:5) uniformly, and then uniformly mixing at 100 DEG C through ultrasonic treatment for 40 min;

[0087] S3, the modified polytetrafluoroethylene base film is prepared by melt blending the hydrophilic polytetrafluoroethylene resin with 5wt% of the lubricant (3MDyneon TF 9205) of the mass of the polytetrafluoroethylene resin, then extruding through an extruder, cooling and forming, extracting, high-temperature bidirectional stretching and high-temperature sintering and curing for 15 min at 350 DEG C;

[0088] S4, the modified polytetrafluoroethylene base film is soaked in an aqueous solution of trimethyladamantane ammonium hydroxide (mass ratio 1:100) for 360 min to improve the affinity of the base film and the emulsion, and then the modified polytetrafluoroethylene base film is dried and laid flat, and the prepared homogeneous casting solution (mass ratio, polysulfone: N, N-dimethylformamide: water = 1:30:1.5) is uniformly coated (100 μm thick) on the modified polytetrafluoroethylene base film, and after standing and drying for 10 min, it is dried and cured in a vacuum drying oven at 50 DEG C for 2 h, and then washed to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

[0089] All material chambers, anode chambers and cathode chambers are independent of each other, and the operating temperature is 45 DEG C.

[0090] The positive plate of the electrolytic cell is a DSA plate, the cation membrane material is a sulfonic acid type Nafion membrane (Nafion N115, Shanghai Hesen Electrical Co., Ltd.), the negative plate is a nickel plate, and the negative plate is treated with tellurium, copper and molybdenum salt (1 mol / L nitrate) at high temperature for 2 h before use to increase the conductivity and reduce the operating voltage, and the current density is 2000 A / m 2 , and the residence time of the electrolytic cell is 40 min.

[0091] The cathode chamber of the electrolytic cell is supplied with 100 mL / min of CO2 gas at a pressure of 0.6 MPa, the anode chamber is fed with KOH at a concentration of 9wt%, and the discharge concentration is 6wt%, the intermediate chamber is fed with KOH at a concentration of 5wt%, and the discharge concentration is 8wt%, and the pressure is 0.25 MPaG.

[0092] Example 4

[0093] The electrolytic device as shown in Figure 1 is used to prepare formic acid from CO2, wherein;

[0094] The modification method of the nanofiltration membrane is as follows:

[0095] S1, adding to 1 L of a solution containing 4 mol / L of benzyltrimethylammonium hydroxide, 48 mol / L of nitrilotriacetic acid (NTA), and 16 mol / L of Na2HPO4 (i.e., a mass ratio of 1:6.7:91.7:22.7) in silicon carbide powder (>1000 mesh, 100 g), a stable dispersion is obtained by ultrasonic treatment (100 W) at room temperature for 1.1 h, then the solution is heated to 70°C, and stirring is performed for 2.5 h to allow sufficient mixing, the obtained mixture is washed with deionized water and ethanol for 2-3 times until the solution is neutral, and after drying, crushing, and sieving >1000 mesh, a surface-modified nanometer boron nitride powder is obtained;

[0096] S2, polyvinyl acetate, surface-modified nanometer silicon carbide powder, and polytetrafluoroethylene (mass ratio of 1:4:6) are uniformly mixed to prepare a hydrophilic polytetrafluoroethylene resin, and the mixture is uniformly mixed by ultrasonic treatment at 70°C for 30 min, and the hydrophilic polytetrafluoroethylene resin is obtained;

[0097] S3, the hydrophilic polytetrafluoroethylene resin is melt-blended with 5 wt% of a lubricant (3M Dyneon TF 9205) based on the mass of the polytetrafluoroethylene resin to obtain a modified polytetrafluoroethylene emulsion, and then the emulsion is extruded through an extruder, cooled, shaped, extracted, high-temperature bidirectional stretched, and sintered and cured at a high temperature of 340°C for 15 min to prepare a modified polytetrafluoroethylene base film;

[0098] S4, the modified polytetrafluoroethylene base film is soaked in an aqueous solution of trimethyladamantylammonium hydroxide (mass ratio of 1:60) for 240 min to improve the affinity of the base film and the emulsion, and then the modified polytetrafluoroethylene base film is dried and laid flat, and a prepared homogeneous casting solution (mass ratio of polysulfone:N,N-dimethylformamide:water

[0099] =1:5:2) is uniformly coated (500 μm thick) on the modified polytetrafluoroethylene base film, and after standing and drying for 10 min, the film is dried and cured in a vacuum drying oven at 50°C for 1 h, and after the heat treatment is completed, the modified polytetrafluoroethylene composite nanofiltration membrane is obtained by washing.

[0100] All material chambers, anode chambers, and cathode chambers are independent of each other, and the operating temperature is 42°C.

[0101] The positive plate of the electrolytic cell is a graphite material, the cation membrane material is carboxylic acid type F-893 (Asahi Glass), the cathode plate is a nickel plate, and the anode plate is treated with tellurium, copper, and molybdenum salts (0.8 mol / L of nitrate) for 1.5 h by high-temperature hydrothermal treatment before use to increase the electrical conductivity and reduce the operating voltage, and the current density is 2200 A / m 2 , and the residence time of the electrolytic cell is 30 min.

[0102] The cathode chamber of the electrolytic cell is supplied with 100 mL / min of CO2 gas at a pressure of 0.6 MPa, the anode chamber is fed with KOH at a concentration of 9 wt%, and the effluent concentration is 5.5 wt%, the intermediate chamber is fed with KOH at a concentration of 5 wt%, and the effluent concentration is 7.5 wt%, and the pressure is 0.25 MPaG.

[0103] Example 5

[0104] The electrolytic device as shown in Figure 1 is used to prepare formic acid from CO2, wherein;

[0105] The modification method of the nanofiltration membrane is as follows:

[0106] S1, silicon carbide powder (>1000 mesh, 100 g) is added to a solution containing 2.5 mol / L benzyltrimethylammonium hydroxide, 20 mol / L iminodiacetic acid, and 10 mol / L KH2PO4 (i.e., mass ratio of 1:4.2:26.6:13.6), a stable dispersion is obtained by ultrasonic treatment (60 W) at room temperature for 1.5 h, then the solution is heated to 90°C and stirred for 2 h to fully mix, the obtained mixture is washed with deionized water and ethanol for 3 times until the solution is neutral, and then the surface-modified nanometer boron nitride powder is obtained by drying, crushing, and sieving to >1000 mesh;

[0107] S2, polyvinyl acetate, surface-modified nanometer silicon carbide powder, and polytetrafluoroethylene (mass ratio of 1:2:6) are uniformly mixed to prepare a hydrophilic polytetrafluoroethylene resin, and the mixture is uniformly mixed by ultrasonic treatment at 130°C for 20 min, to obtain the hydrophilic polytetrafluoroethylene resin;

[0108] S3, the hydrophilic polytetrafluoroethylene resin is melt-blended with a lubricant (Henggao Letai 30138) accounting for 5 wt% of the mass of the polytetrafluoroethylene resin to obtain a modified polytetrafluoroethylene emulsion, and then the modified polytetrafluoroethylene emulsion is extruded by an extruder, cooled, shaped, extracted, high-temperature bidirectional stretched, and sintered and cured at a high temperature of 360°C for 10 min to prepare a modified polytetrafluoroethylene base film;

[0109] S4, the modified polytetrafluoroethylene base film is soaked in an aqueous solution of trimethyladamantylammonium hydroxide (mass ratio of 1:80) for 110 min to improve the affinity of the base film and the emulsion, and then the modified polytetrafluoroethylene base film is dried and laid flat, a prepared homogeneous casting solution (mass ratio, polysulfone:N,N-dimethylformamide:water = 1:20:4) is uniformly coated (200 μm thick) on the modified polytetrafluoroethylene base film, and after standing and drying for 10 min, the modified polytetrafluoroethylene base film is dried and cured in a vacuum drying oven at 60°C for 3 h, and then washed to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

[0110] All material chambers, anode chambers, and cathode chambers are independent of each other, and the operating temperature is 48°C.

[0111] The positive plate of the electrolytic cell is a DSA plate, the cation membrane material is F-893 (Asahi), the negative plate is a nickel plate, and the negative plate is treated with tellurium, copper, and molybdenum salts (1 mol / L nitrate) for 2 h at high temperature and water for the purpose of increasing the conductivity and reducing the operating voltage. The current density is 1800 A / m 2 , and the residence time of the electrolytic cell is 50 min.

[0112] The cathode chamber of the electrolytic cell is supplied with 100 mL / min CO2 gas at a pressure of 0.6 MPa, the anode chamber is fed with KOH at a concentration of 9 wt%, and the effluent concentration is 6.5 wt%, the intermediate chamber is fed with KOH at a concentration of 5 wt%, and the effluent concentration is 8.5 wt%, and the pressure is 0.25 MPaG.

[0113] Comparative Example 1

[0114] The operating conditions are the same as in Example 3, except that the nanofiltration membrane is not used, i.e., the nanofiltration membrane and the intermediate chamber are removed, the anode chamber is fed with KOH at a concentration of 9 wt%, and the effluent concentration is 5-7 wt%, and the cathode chamber is fed with CO2 and water.

[0115] Comparative Example 2

[0116] The operating conditions are the same as in Example 3, except that the cation membrane is not used, i.e., the cation membrane and the intermediate chamber are removed, the anode chamber is fed with KOH at a concentration of 9 wt%, and the effluent concentration is 5-7 wt%, and the cathode chamber is fed with CO2 and water.

[0117] Comparative Example 3

[0118] The operating conditions are the same as in Example 3, except that the cathode plate is not treated.

[0119] Comparative Example 4

[0120] The operating conditions are the same as in Example 3, except that the nanofiltration membrane is not modified.

[0121] The electrolytic devices of the above examples and comparative examples are used to prepare formic acid by CO2 electrolysis, and the experimental conditions are as follows: the cathode chamber of the electrolytic cell is supplied with 100 mL / min CO2 gas at a pressure of 0.6 MPa, the anode chamber is fed with KOH at a concentration of 9 wt%, and the effluent concentration is 5-7 wt%, the intermediate chamber is fed with KOH at a concentration of 5 wt%, and the effluent concentration is 7-9 wt%, the pressure is 0.25 MPaG, and the service life is calculated based on a 30% increase in voltage.

[0122] The electrolytic reaction results of the above examples and comparative examples are shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] From the above table, it can be seen that the cation membrane, modified nanofiltration membrane and modified cathode have great improvement in the conversion rate of CO2, reduction of electrolysis voltage and improvement of operation life.

[0127] Those skilled in the art can understand that, under the teaching of the present specification, some modifications or adjustments can be made to the present application. These modifications or adjustments should also be within the scope defined by the claims of the present application.

Claims

1. A method for the production of formic acid by electrolysis of CO2 in a three-compartment two-membrane cell, characterized in that, The application relates to a method for preparing potassium formate by electrolysis. The electrolytic device comprises a cation membrane and a nanofiltration membrane, which separate an electrolytic cell into an anode chamber, an intermediate chamber and a cathode chamber; an anode plate is arranged on the side of the anode chamber far from the cation membrane, and a cathode plate is arranged on the side of the cathode chamber far from the nanofiltration membrane; the anode plate and the cathode plate are connected with a power supply; A first KOH aqueous solution is added into the anode chamber, a second KOH aqueous solution is added into the intermediate chamber, and CO2 and water are introduced into the cathode chamber; after the power supply is turned on and fully reacted, KOH solutions are obtained in the anode chamber and the intermediate chamber respectively, and KCOOH products are obtained in the cathode chamber.

2. The method of claim 1, wherein, The cation membrane is one or more of a sulfonic acid type, a phosphoric acid type, a carboxylic acid type and a composite cation membrane.

3. The method of claim 1, wherein, The mass concentration of the first KOH aqueous solution is higher than that of the second KOH aqueous solution, and the absolute value of the concentration difference is not less than 2%. Preferably, the mass concentration of the first KOH aqueous solution is 5-9%, and the mass concentration of the second KOH aqueous solution is 5-7%. More preferably, the mass concentration of the KOH solution obtained in the anode chamber is lower than that of the first KOH aqueous solution, and the mass concentration of the KOH solution obtained in the intermediate chamber is higher than that of the second KOH aqueous solution. Further preferably, the mass concentration of the KOH solution obtained in the anode chamber is 3-7%, and the mass concentration of the KOH solution obtained in the intermediate chamber is 7-9%.

4. The method of claim 1, wherein, The nanofiltration membrane is a modified nanofiltration membrane, and the modification method is as follows: S1. A quaternary amine base, a complexing agent and a pH buffer are added into silicon carbide powder, a stable dispersion is obtained through ultrasonic treatment, then the solution is heated and stirred to fully mix, the obtained mixture is washed with deionized water and alcohol until the solution is neutral, and then the mixture is dried, crushed and sieved to obtain nanometer silicon carbide powder with surface-modified quaternary amine base; S2. Polyolefin ester monomer, nanometer silicon carbide powder with surface-modified quaternary amine base and polytetrafluoroethylene resin are uniformly mixed and then uniformly mixed through ultrasonic treatment to obtain hydrophilic polytetrafluoroethylene resin; S3. The hydrophilic polytetrafluoroethylene resin is melt-blended with a lubricant to obtain modified polytetrafluoroethylene emulsion, and then the modified polytetrafluoroethylene emulsion is extruded through an extruder, cooled, extracted to remove solvent, high-temperature bidirectional stretched and high-temperature sintered to obtain a modified polytetrafluoroethylene base film; S4. The modified polytetrafluoroethylene base film is soaked in a trimethyladamantane ammonium hydroxide aqueous solution, then the modified polytetrafluoroethylene base film is dried and laid flat, a prepared homogeneous casting solution is uniformly coated on the modified polytetrafluoroethylene base film, and then the modified polytetrafluoroethylene base film is placed, dried and solidified, and washed to obtain a modified polytetrafluoroethylene composite nanofiltration membrane.

5. The method of claim 4, wherein, In step S1, the quaternary amine base is at least one of benzyltrimethylammonium hydroxide, hexamethonium hydroxide and trimethyladamantane ammonium hydroxide, preferably benzyltrimethylammonium hydroxide; the complexing agent is at least one of EDTA, iminodiacetic acid and nitrilotriacetic acid (NTA), preferably EDTA; and the pH buffer is at least one of Na2HPO4 and KH2PO4, preferably Na2HPO4. Preferably, the concentration of the quaternary amine base is 2-5 mol / L, the concentration of the complexing agent is 10-100 mol / L, and the concentration of the pH buffer is 4-25 mol / L; More preferably, the mass ratio of the quaternary amine base, the complexing agent, and the pH buffer is 1:5:2-1:20:5; and / or In step S1, the ultrasonic treatment time is 1-1.5 h, and then the solution is heated to 60-90℃ and stirred for 2-4 h.

6. The method according to claim 4 or 5, characterized in that, In step S2, the ultrasonic treatment temperature is 60-130℃, and the treatment time is 20-60 min; Preferably, in step S3, the high-temperature sintering temperature is 330-360℃, and the sintering time is 10-20 min; Preferably, in step S4, the soaking time is 60-480 min, the standing time is at least 10 min, the drying and solidifying temperature is 50-80℃, and the drying time is 1-3 h.

7. The method of claim 1, wherein, The anode chamber, the intermediate chamber, and the cathode chamber are independent of each other, and the operating temperature is 40-50℃.

8. The method of claim 1, wherein, The anode plate is one or more of a nickel plate, a DSA plate, and a graphite material.

9. The method according to claim 1 or 8, characterized in that, The cathode plate is one or more of a nickel plate and a graphite material; Preferably, the cathode plate is soaked in a tellurium salt, a copper salt, or a molybdenum salt at high temperature and hydrothermally for 1-3 h before use. More preferably, the tellurium salt, the copper salt, and the molybdenum salt are nitrate salts at a concentration of 0.2-2 mol / L.

10. The method of claim 1, wherein, The electrolysis device has a current density of 1500-2500 A / m 2 and a residence time of 20-60 min.

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